Lua Requires Chilkat v11.6.0+

Argon2 Key Derivation with a Secret (Pepper), AD, and Encodings

Demonstrates the optional Argon2 options for Crypt2.Argon2DeriveKey: secret (a pepper), ad (associated data), the encoding member and its per-member overrides saltEncoding/secretEncoding/adEncoding, passwordCharset, and maxMemoryKb.

Background. A pepper is a secret value held by the application and not stored with the hash, so a stolen hash database cannot be attacked without it. The encoding members control how the salt, secret, and ad text are interpreted as bytes (base64 by default; utf-8 uses the characters themselves). maxMemoryKb is a guard against an unreasonable memory cost.

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Lua

local chilkat = require("chilkat")

local crypt = chilkat.Crypt2.new()

-- The password should come from a secure source rather than being hard-coded.
local password = "correct horse battery staple"

-- Build the Argon2 options JSON, this time using the optional secret, ad, and encoding members.
--   secret         the RFC 9106 secret value K, often called a "pepper": a key held by the
--                  application and NOT stored with the hash, so a stolen hash database cannot be
--                  attacked without it.
--   ad             optional associated data X: additional non-secret data bound into the derivation.
--   encoding       how salt, secret, and ad are encoded (default base64).  Per-member overrides are
--                  saltEncoding, secretEncoding, and adEncoding.
--   passwordCharset  the charset the password is converted to before use (default utf-8).
--   maxMemoryKb    a guard (not an Argon2 parameter) refusing to allocate more than this many KB;
--                  default 2097152 (2 GB).
local json = chilkat.JsonObject.new()

-- The salt is provided here as hex, overriding the default base64 for just this member.
json:update_string("salt", "0102030405060708090a0b0c0d0e0f10")
json:update_string("saltEncoding", "hex")

-- The pepper is supplied as UTF-8 text (its own characters are the bytes).
json:update_string("secret", "application-wide-pepper")
json:update_string("secretEncoding", "utf-8")

-- Associated data, supplied as UTF-8 text.
json:update_string("ad", "user-id-42")
json:update_string("adEncoding", "utf-8")

json:update_string("passwordCharset", "utf-8")
json:update_int("maxMemoryKb", 1048576)
json:update_int("keyLen", 32)

local bdKey = chilkat.BinData.new()
local success = crypt:argon2_derive_key(password, json:emit(), bdKey)
if not success then
    print(crypt.last_error_text)
    return
end

local keyHex = bdKey:get_encoded("hex")
if not bdKey.last_method_success then
    print(bdKey.last_error_text)
    return
end

print("Derived key: " .. keyHex)